The invention relates to an organic light-emitting illuminant and to a coating device for producing it, and to a method for producing it.
Organic light-emitting illuminants, in particular organic light-emitting diodes (OLEDs), are currently already being used in many areas of consumer electronics, for example in display applications, and are also regarded as a future technology in the lighting sector. An OLED structure contains one or more light-emitting organic layers (EML) arranged between two electrodes, for example a cathode and an anode on a substrate.
According to the prior art, two designs of organic light-emitting diodes are known, depending on the direction of the light emission. It is possible to produce OLEDs having the light emission away from the substrate, in the so-called top emission geometry, or OLEDs having the light emission through the substrate, in bottom emission geometry.
FIG. 1 indicates a schematic construction of an OLED in top emission geometry known from the prior art. It consists of a non-transparent substrate 100, on which are constructed in sequence an optional smoothing layer 101, a first electrode layer 102, which in FIG. 1 corresponds to the anode, an organic layer stack comprising a hole transport layer 103 (HTL), at least one, preferably two or three, separate, vertically constructed emission layers 104 (EML), which emit light in each case in a different color, for example red, green or blue, and comprising an electron transport layer 105 (ETL), and also a semitransparent metallic electrode layer 106, which in FIG. 1 corresponds to the cathode. Hole and electron transport layers are also referred to in combination as charge carrier transport layers. Further transparent layers, e.g. buffer layers, can optionally be present between the layers mentioned. When a voltage is applied between a first and second electrode layer, light quanta of different colors are generated in the emission layers and can leave the component through the semitransparent cathode.
In contrast to OLEDs in top emission geometry, the OLEDs in bottom emission geometry have a light-transparent substrate, on which a first light-transparent electrode layer and a second light-reflecting electrode are deposited, such that emission can take place through the substrate, i.e. in the bottom direction.
The order of the layers anode/HTL/EBL/EML/HBL/ETL/cathode, formed on the substrate, can also be reversed, in principle, in which case the electrode on the light exit side should then respectively be embodied as semitransparent or transparent.
Furthermore, OLED illuminants are known in which regions which emit light in different colors are arranged alongside one another in order to generate a white light emission. By way of example, if two mutually adjacent regions emit light in different colors, this should be understood to mean that one region emits light in a first color and the second region emits light in a second color, the first and second colors being different. By means of additive mixing of the light colors of the individual regions, a specific, for example a white, color impression can be set for the observer by means of a suitable choice of the individual colors and of the respective light intensities. In this case, each of the regions has the following layer construction containing a substrate, a first electrode, an organic layer stack and an electrode, wherein the organic layer stack has a hole transport layer, an emission layer that emits monochrome light, and an electron transport layer. The layer sequence of the organic layers corresponds to the layer construction with the anode as first electrode constructed on the substrate. A different sequence of the organic layers, which has an electron transport layer, an emission layer that emits monochrome light, and a hole transport layer corresponds to the layer construction with the cathode as first electrode. Optionally, the two variants of the layer construction can have, for each of the regions, a smoothing layer formed on the substrate.
Optionally, the OLED layer construction can also have further functional layers and layer sequences known from the prior art, for example layers that are arranged above the top electrode and are effective as a barrier to water vapor and oxygen, mechanical protective layers or optically active layers or structures that intensify the coupling-out of light.
In the top emission geometry structures, the interaction of a reflective electrode, intervening transparent layers and a semitransparent electrode results in the formation of an optical cavity and, as a result of interference effects, in a great dependence of the light intensity coupled out through the top electrode on the aggregate layer thickness of the transparent layers, such as the hole transport layer (HTL), the emission layer (EML), and electron transport layer (ETL), also called HTL, EML and ETL hereinafter. In this case, for each of the emission layers there exist optima of the aggregate layer thickness, the so-called coupling-out maxima, for which the emitted quantity of light assumes maximum values.
This effect is likewise present in the bottom emission geometry, to an attenuated extent owing to the more transparent electrode, since differences in refractive index at different boundary layers between the OLED layers and the substrate or else within the OLED layer system likewise exhibit a thickness-dependent change in the coupling-out of light.
The thickness optima for the different emission colors have different values, such that optimum light coupling-out conditions cannot be set for each of the emission colors when optimizing the layer thicknesses.
The object of the present invention is to provide OLED structures which have an improved intensity of the light emission. In this case, the intention is to increase the efficiency of coating devices for producing OLED illuminants of this type. In this case, production is intended to be cost-effectively and commercially applicable.